The invention relates to a process for the joining of strips and/or sheets of metallic materials, wherein at least two strips and/or sheets are introduced offset from one another with reference to their longitudinal axes and overlapping one another and converging on one another at an acute angle into a roll nip and are pressed on to one another in a roll pass, so that they are completely or partially rigidly connected to one another at their surfaces brought into contact.
Processes of the kind specified are used, for example, to provide steel sheets with metal coatings. Such coatings are used for protection against corrosion and wear, to enhance surface hardness, give a more decorative appearance, to improve sliding properties or for the application of material to places liable to wear. The coatings can have different thicknesses, in dependence on the process and the materials used.
In a prior art process of the kind specified, namely a cold pressure welding process, soft unalloyed steel or stainless steel is given a cladding with aluminium, copper or brass by cold rolling. As a rule thin strips or sheets up to thicknesses around 4 mm are obtained. To obtain a satisfactory connection between the different metals, reshaping is required in the contact zone. Such reshaping opens up oxide layers or surface films, so that metals not vet exposed to the surrounding atmosphere are connected to one another. This so-called cladding lamination requires a threshold change of shape of usually at least 30% in one cold rolling pass. For this purpose high rolling forces must be used. Heavy demands are also made on the surfaces in the cladding zone; these must be previously suitably cleaned. As a result, the process is expensive in technical apparatus. Moreover, the combinations of materials suitable for cold rolling cladding are limited (Journal "Aluminium", 56, 1980.2, pages 147/149).
Another known cold pressure welding process is the explosive cladding of unalloyed, low-alloyed or stainless steel with other metallic materials. A cladding of various materials is applied directly or via intermediate layers. Explosive claddings usually have thicknesses above 4 mm. One example is the explosive-clad transition members (transition joints) for welded connections between constructional steel and the fairly high-strength aluminium alloy AlMg 4.5, which must be carried out using an intermediate layer of Al 99.5, to achieve those utilization properties which are required of fusion welding connections with transmission of force perpendicularly to the plane of the cladding. In this process the advantage of a certain independence as regards the combinations of materials is offset by the disadvantage that a number of layers must be joined. This kind of strip production is therefore also bound up with the presence of expensive devices Journal "Aluminium", 56, 1980.2, pages 147/149).
It is also known to connect steel and aluminium to one another by fusion welding. Conventional welding processes are used such as the TIG or the MIG process. In any case the process is so performed that only aluminium in the liquid state is present in the roil nip. A disadvantage of this process is that at the boundary layer of the two materials an intermetallic connection is formed which is the weakest point of the welded connection (Journal "Aluminium", 56, 1980.2, pages 147/149).
In another known Joining process, also a fusion welding, the energy required for melting is introduced into the roll nip by means of a laser beam. In this known process both the carts to be joined are melted. If in this process aluminium and steel are to be connected to one another, the same problems probably arise as in the case of the other melting processes (DE 37 13 975 A1).
Lastly, a process is known for guiding metal strips together wherein the two strips are introduced converging on one another into a roll nip and are pressed on to one another in a roll pass, so that they are rigidly connected to one another at their surfaces brought into contact. Immediately prior to physical contact in the roll nip, the strips to be brought into contact are heated by a laser beam, the heated zone being either melted or merely heated to a diffusion temperature (U.S. Pat. No. 4,471,204). However, according to that prior art the two strips to be guided together are laterally offset in relation to their axes and overlap one another. In such cases there is a risk that the softer strip will be squashed in the projecting zone in the roll nip.
It is an object of the invention to provide a process for the connection of overlaoding strips of different metallic materials of difficult fusion meltability, if any, which is less expensive than the aforementioned process and wherein no squashing takes place of the overlapping zone of the strip or sheet of a softer material.